During the past decade researchers have begun to lay a solid foundation for performing gene therapy related procedures. For example, long-term expression of heterologous genes in mammals was demonstrated using viral vectors engineered to contain tissue specific promoters (U.S. Pat. No. 6,040,172, herein specifically incorporated by reference in its entirety). In addition, a modification of behavior was demonstrated in an animal model for human Parkinson's Disease (U.S. Pat. No. 6,180,613, herein specifically incorporated by reference in its entirety). However, before gene therapy becomes a general medical practice, other factors must be addressed. One such factor concerns the regulation of the expression of the genetic transcript and/or the resulting gene product.
For example, many gene therapy strategies involve the expression of genes which are likely to cause adverse effects if they are expressed continuously. Thus, administering a gene transcript that is incapable of being regulated will oftentimes be unacceptable. In such cases, performing gene therapy with a regulatable gene expression system is necessary to control the expression of the otherwise therapeutic gene and/or gene product. Presently, regulatable promoters such as the metallothionein promoter, the tetracycline-on, and the tetracycline-off promoters are available. Unfortunately, such promoters are not well-suited for gene therapy because they are controlled by inducer compounds that are either toxic or can become toxic with long-term use. Still others are not practical for specific in vivo applications, e.g., they cannot cross the blood-brain barrier. Generally, the regulatable promoters that are currently employed in gene therapy strategies have been identified/selected for very different purposes and have therefore not been optimized for the particular role they must play in gene therapy.
Therefore, there is a need for developing methods for identifying genetic regulatory sequences (e.g., a promoter) that will be responsive to a stimulus in a particular tissue. In addition, there is a need for identifying stimulants of such genetic regulatory sequences that are both non-toxic and can readily gain access to the target tissue. There is a need for developing vectors that employ such genetic regulatory sequences for use in gene therapy. Further, there is a need to provide methods of performing gene therapy which employ the novel stimulants and genetic regulatory sequences of the present invention.